Immunologic reactions which result in formation of antibodies against autologous blood cells have been studied to determine the significance of immunity in development of "idiopathic" blood cell deficiency states. Of special interest have been the biochemical reactions which result in formation of complexes between cells, antibodies and drug haptenes, and the physiologic processes which result in sequestration of blood cells sensitized by antibodies. Work has continued on identifying the inherited leukocyte and platelet isoantigens that are also known as transplantation of HLA antigens. Immunologic techniques have been used to develop diagnostic tests for infectious diseases such as hepatitis and toxoplasmosis and there has been a continued interest in evaluating hepatitis immunity. Studies have continued on the serology of platelet deficiency states, particularly post-transfusion and neonatal purpura, and on developing tests for detecting antibodies that do not react in more conventional immunologic systems.